HR issue founded on epix2

I have the exact same situation.  I wear an Apple Watch 7 on my left wrist and Epix 2 on my right wrist.  I upgraded from a Fenix 6X Pro Solar. If I don't tell the Apple Watch I am exercising it can often completely miss reporting and recognizing the activity but if I initiate the activity on the Apple Watch 7 it produces virtually identical results to the Fenix 6X Pro Solar.  I am finding the same issue you have found that the Epix 2 is getting some activities completely wrong.  For 30 to 60 minutes of indoor cycling, the Apple Watch 7 and Epix 2 report the same average heart rate.  When I am jumping rope, the Apple Watch is reporting an average of 129 bpm (which seems right) but the Epix 2 is reporting an average of 154 bpm and max of 172 (which is definitely too high).  So like in your case, the Epix 2 is doing something wrong for the cardio exercise when it is jump rope.  For trail running, the Garmin was 12 bpm higher on one 6-mile run and 2 bpm lower on another 6-mile run.  

So there is clearly a bug, at least for the cardio activity.  I don't know if it is hardware or software, but I am going to keep it (so I guess I am assuming it software that can be fixed in an update).

Sean

100 beats per minute sounds WAY too low for a jumprope workout. So I am actually more skeptical of your Instinct.

Have you ever tried to figure out your max heart rate?

I have the same problem with the "Yoga" activity, heart rate was 134 bpm on the Epix, way too high. Seems like counting it twice. If I stop the activity, the heart rate is reliable again with normal values (62 bpm in this case) 

@nonparametric   he mentioned over 180 not 100 :)

No... he/she said that their Instinct was reporting a heart rate of 100 while doing a jump rope workout, and they believe that to be a more reasonable value. Having jumped a rope once or twice in my life, that seems incredibly unlikely to me.

Garmin recommend wearing watches with optical heart rate above the wrist bone for best results. From your photos it looks like the watches are on the wrist bone thereby making a good reading difficult - https://support.garmin.com/en-US/?faq=xQwjQjzUew4BF1GYcusE59. The link also explains some of the inherent limitations of optical heart rate. These have been well discussed ever since the first watches with optical heart rate were released some years back. First thing to do is to wear the watch clear of the wrist bone and tighten it a notch or two tighter than when you are rest.

That said technology has moved on and for me at least, I can exercise without a chest strap 90% of the time and be confident the numbers are correct. But activities like jump rope and rowing are always going to be a challenge.

Sounds like your instinct is not detecting HR well. That looks like a non solar instinct to me the HR sensor on them is quite a few years old now and not as good as the two new generations above it. 

100hr is very low for jump rope!!

You have a VERY small wrist.  You probably are getting a lot of jigglle with a heavier watch. Wear it higher up on your arm or get a lighter, smaller watch.  The Black Sapphire one is the lightest and it doesn't have any wiggle for me, whilst the AW7 was heavier and wiggled.  But, I never had WHR issues with the AW.

I have big body structure.  6'2 210lb.   So the Epix sets nicely on my wrist.  The Heart rate for me has been spot on running and swimming laps.

Had the same isue with my 6Xsaphire and the solution was that the watch must have a tight fit, after that it have been fantastic. Ready for the Epix 2 now.

I don't know anything about OP's physical stats, but I could easily hit 150bpm average and 180bpm peak while doing jumprope. I'm not sure why they think that's impossible. 100bpm seems way more unlikely.